🐞 CI unit tests require etcd

Previously `etcd` wasn't running, causing the integration tests to fail
because they require `etcd`.

We now run `etcd`.

In the future I plan to add the ability to not require `etcd`, to use a
local table of key-value pairs, but I don't plan to test that option in
CI. It'll be for the very few users who use the sslip.io code but not
the  service.

fixes <https://ci.nono.io/teams/main/pipelines/sslip.io/jobs/unit/builds/23>:
```
{"level":"warn","ts":"2021-12-31T01:34:28.089Z","logger":"etcd-client","caller":"v3@v3.5.1/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0001ef340/localhost:2379","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = latest balancer error: last connection error: connection error: desc = \"transport: Error while dialing dial tcp 127.0.0.1:2379: connect: connection refused\""}

2021/12/31 01:34:28 couldn't GET "dmy-key": context deadline exceeded
```

ci/pipeline-sslip.io.yml

@@ -20,10 +20,10 @@ jobs:
       - name: sslip.io
       run:
         dir: sslip.io/src/sslip.io-dns-server
-        path: ginkgo
+        path: zsh
         args:
-        - -r
+        - -c
-        - .
+        - etcd > /dev/null 2>&1 & ginkgo -r .
 - name: dns-servers
   public: true
   plan: